Flexible display device

ABSTRACT

A flexible display device including a flexible display panel, a flexible outer member disposed on the flexible display panel, and an adhesive member disposed between the flexible display panel and the flexible outer member. An elastic modulus of the adhesive member is from about 1/1000000 to about 1/1000 of an elastic modulus of each of the flexible display panel and the flexible outer member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. non-provisional patent application is a Continuation of U.S.patent application Ser. No. 14/579,491, filed Dec. 22, 2014, whichclaims priority to and the benefit of Korean Patent Application No.10-2014-0004091, filed on Jan. 13, 2014, each of which is herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND Field

The present disclosure relates to a flexible display device. Moreparticularly, the present disclosure relates to a flexible displaydevice capable of reducing defects.

Discussion of the Background

In recent years, a curved display device (hereinafter, referred to as aflexible display device) has been developed. The flexible display deviceincludes a flexible display panel and various outer members.

The outer members serve different purposes. The outer members aredisposed on at least one or two opposing surfaces of the flexibledisplay panel and are bendable to match the curvature of the flexibledisplay panel.

The above information in this Background section is only for enhancementof understanding of the background of the invention and, therefore, itmay contain information that does not constitute prior art.

SUMMARY

The present disclosure provides a flexible display device having reducedstrain during use.

Embodiments of the inventive concept provide a flexible display deviceincluding a flexible display panel, a flexible outer member disposed onthe flexible display panel, and an adhesive member disposed between theflexible display panel and the flexible outer member. An elastic modulusof the adhesive member is from about 1/1000000 to about 1/1000 of anelastic modulus of each of the flexible display panel and the flexibleouter member.

When the flexible display device is bent, different neutral planes arerespectively defined in the flexible display panel and the flexibleouter member. A compressive stress applied to the neutral plane definedin the display panel is substantially equal to a tensile stress appliedto the neutral plane defined in the display panel, and a compressivestress applied to the neutral plane defined in the outer member issubstantially equal to a tensile stress applied to the neutral planedefined in the outer member.

Exemplary embodiments of the inventive concept provide a flexibledisplay device including an adhesive member having an elastic modulus ofabout 0.01 MPa to about 1 MPa, a flexible display panel having anelastic modulus of about 1 GPa to about 10 GPa, and a flexible outermember having an elastic modulus of about 2 GPa to about 7 GPa.

Exemplary embodiments of the inventive concept provide a flexibledisplay device including a flexible display panel, flexible outermembers disposed on the flexible display panel, and an adhesive memberdisposed every between two adjacent outer members to each other amongthe flexible display panel and the flexible outer members. The adhesivemember has an elastic modulus of about 1/1000000 to about 1/1000 of anelastic modulus of each of the two adjacent outer members to each other.

According to the above, when the flexible display device is bent,different neutral planes are respectively defined in the flexibledisplay panel and the flexible outer member. This is because theflexible display panel and the flexible outer member are partiallydecoupled from each other by the stress applied to the adhesive member,when the flexible display device is bent.

When the flexible display device is bent, the flexible display panel andthe flexible outer member have independent strains. The strains of theflexible display panel and the flexible outer member are small inconsideration of the thickness of the flexible display device. Each ofthe flexible display panel and the flexible outer member has the straincorresponding to its thickness. Accordingly, although the flexibledisplay device is bent, internal components of the flexible displaypanel and the flexible outer member are not damaged. In addition, theflexible display panel and the flexible outer member are not physicallydecoupled from each other.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention. The above and other advantages of the present disclosure willbecome readily apparent by reference to the following detaileddescription when considered in conjunction with the accompanyingdrawings.

FIG. 1 is a perspective view showing a flexible display device that isin an unfolded state, according to an exemplary embodiment of thepresent disclosure.

FIG. 2 is a plan view showing a flexible display panel according to anexemplary embodiment of the present disclosure.

FIG. 3 is an equivalent circuit diagram showing a pixel according to anexemplary embodiment of the present disclosure.

FIG. 4 is a cross-sectional view showing a pixel according to anexemplary embodiment of the present disclosure.

FIGS. 5A and 5B are cross-sectional views showing a neutral planeoccurring in flexible display devices when the flexible display devicesare bent.

FIG. 6 is a graph showing strain of the flexible display devices shownin FIGS. 5A and 5B.

FIG. 7 is a cross-sectional view showing a flexible display deviceaccording to an exemplary embodiment of the present disclosure.

FIGS. 8A to 8F are cross-sectional views showing flexible displaydevices according to exemplary embodiments of the present disclosure.

DETAILED DESCRIPTION

Aspects of the present disclosure are described more fully hereinafterwith reference to the accompanying drawings, in which exemplaryembodiments of the invention are shown. This invention may, however, beembodied in many different forms and should not be construed as limitedto the exemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure is thorough, and willfully convey the scope of the invention to those skilled in the art. Inthe drawings, the size and relative sizes of layers and regions may beexaggerated for clarity. Like reference numerals in the drawings denotelike elements.

It will be understood that when an element or layer is referred to asbeing “on”, “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layeror intervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on,” “directly connected to”or “directly coupled to” another element or layer, there are nointervening elements or layers present. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one element, component, region, layer or section fromanother region, layer or section. Thus, a first element, component,region, layer or section discussed below could be termed a secondelement, component, region, layer or section without departing from theteachings of the present invention.

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms, “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “includes”and/or “including”, when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Hereinafter, the present invention will be explained in detail withreference to the accompanying drawings.

FIG. 1 is a perspective view showing a flexible display device that isunfolded according to an exemplary embodiment of the present disclosure.The flexible display device may be curved or rolled over the entire areathereof, or may be bent in a specific area thereof.

Referring to FIG. 1, the flexible display device (hereinafter, referredto as a display device) includes a flexible display panel DP(hereinafter, referred to as a display panel) and an outer member OSMdisposed on the display panel DP. The display panel DP and the outermember OSM are coupled to each other by an adhesive member AM.

The display panel DP includes a display surface DS defined by a firstdirection DR1 and a second direction DR2. The display panel DP displaysan image through the display surface DS. FIG. 1 shows the display panelDP including the display surface DS as a representative example.

The adhesive member AM is disposed on the display surface DS. The outermember OSM is disposed on the adhesive member AM. The display panel DPand the outer member OSM are spaced apart from each other in a thicknessdirection DR3 (hereinafter, referred to as a third direction DR3), suchthat the adhesive member AM is disposed between the display panel DP andthe outer member OSM. According to another exemplary embodiment, theouter member OSM may be disposed on a non-display surface NDS facing thedisplay surface DS.

The outer member OSM may include at least one of a touch screen panel,an optical member, a window member, and a protective member. The touchscreen panel, the optical member, the window member, and the protectivemember may be stacked in the third direction DR3.

The adhesive member AM may be an adhesive layer manufactured by coatingan liquid adhesive material, which is then cured, or may be a separatelymanufactured adhesive sheet. For instance, the adhesive member AM may bea pressure sensitive adhesive sheet. The pressure sensitive adhesivesheet includes a polymer, a cross-linking agent, and a resin. Thepolymer may include one or more of an acryl-based polymer, asilicon-based polymer, and a urethane-based polymer.

The display panel DP includes a flexible base substrate (not shown),signal lines (not shown) disposed on the base substrate, and pixels (notshown) electrically connected to the signal lines. The pixels generatethe image on the basis of signals provided through the signal lines. Thedisplay panel DP may be an organic light emitting display panel, anelectrophoretic display panel, or an electrowetting display panel.

The display device is bent along a bending axis PA. The bending axis PAis an imaginary axis extending in the second direction DR2. When thedisplay device is bent, stress occurs in the display device.

The display panel DP, the adhesive member AM, and the outer member OSMhave different elastic modulus (or Young's modulus). Each of the displaypanel DP, the adhesive member AM, and the outer member OSM is deformedto correspond to its elastic modulus by the stress occurring when thedisplay device is bent.

Each of the display panel DP, the adhesive member AM, and the outermember OSM has the elastic modulus determined depending on its layerstructure and/or material composition. Hereinafter, a relation betweenthe layer structure of the display panel DP and the elastic modulus ofthe display panel DP will be described in detail.

FIG. 2 is a plan view showing a flexible display panel according to anexemplary embodiment of the present disclosure, FIG. 3 is an equivalentcircuit diagram showing a pixel according to an exemplary embodiment ofthe present disclosure, and FIG. 4 is a cross-sectional view showing apixel according to an exemplary embodiment of the present disclosure.FIGS. 2 to 4 show the organic light emitting display panel.

Referring to FIG. 2, the display panel DP includes a plurality of lightemitting areas LA(i, j) to LA(i+1, j+2) and a non-light emitting areaNLA surrounding the light emitting areas LA(i, j) to LA(i+1, j+2). FIG.4 shows six light emitting areas LA(i, j) to LA(i+1, j+2), as arepresentative example.

Display elements (not shown) of the pixels (not shown) are disposed tooverlap the light emitting areas LA(i, j) to LA(i+1, j+2), respectively,when viewed in a plan view. Circuit parts (not shown) of the pixels aredisposed to overlap with the non-light emitting area NLA, when viewed ina plan view. In addition, the signal lines are disposed to overlap withthe non-light emitting area NLA, when viewed in a plan view.

FIG. 3 shows the equivalent circuit diagram of the pixel PX(i, j). Thepixel PX(i, j) receives a gate signal from an i-th gate line GLi and adata signal from a j-th data line DLj. The pixel PX(i, j) receives afirst source voltage ELVDD from a source voltage line KL.

The pixel PX(i, j) includes an organic light emitting diode OLED as thedisplay element. The pixel PX(i, j) includes a switching thin filmtransistor TR-S, a driving thin film transistor TR-D, and a capacitorCap, as a circuit part to drive the organic light emitting diode OLED.

The switching thin film transistor TR-S outputs the data signal appliedto the j-th data line DLj, in response to the gate signal applied to thei-th gate line GLi. The capacitor Cap is charged with a voltagecorresponding to the data signal provided from the switching thin filmtransistor TR-S.

The driving thin film transistor TR-D is connected to the organic lightemitting diode OLED. The driving thin film transistor TR-D controls adriving current flowing through the organic light emitting diode OLED,in response to the amount of electric charge stored in the capacitorCap. The organic light emitting diode OLED emits the light during theturn-on period of the driving thin film transistor TR-D.

FIG. 4 shows a cross-sectional view of a portion of the equivalentcircuit shown in FIG. 3. Referring to FIG. 4, insulating layers 10, 20,and 30, the driving thin film transistor TR-D, and the organic lightemitting diode OLED are disposed on the base substrate SUB.

The base substrate SUB includes a flexible plastic substrate. Asemiconductor pattern AL of the driving thin film transistor TR-D isdisposed on the base substrate SUB. A first insulating layer 10 isdisposed on the base substrate SUB to cover the semiconductor patternAL. The first insulating layer 10 includes an organic layer and/or aninorganic layer. The first insulating layer 10 may include a pluralityof thin layers.

A control electrode GE (or gate electrode) of the driving thin filmtransistor TR-D is disposed on the first insulating layer 10. The secondinsulating layer 20 is disposed on the first insulating layer 10 tocover the control electrode GE. The second insulating layer 20 includesan organic layer and/or an inorganic layer. The second insulating layer20 may include a plurality of thin layers.

An input electrode SE (or source electrode) and an output electrode DE(or drain electrode) of the driving thin film transistor TR-D aredisposed on the second insulating layer 20. The input electrode SE andthe output electrode DE are connected to the semiconductor pattern ALrespectively through a first contact hole CH1 and a second contact holeCH2 respectively. The first contact hole CH1 and the second contact holeCH2 are formed through the first and second insulating layers 10 and 20.According to another embodiment, the driving thin film transistor TR-Dmay have a bottom gate structure.

The third insulating layer 30 is disposed on the second insulating layer20 to cover the input electrode SE and the output electrode DE. Thethird insulating layer 30 includes an organic layer and/or an inorganiclayer. The third insulating layer 30 may include a plurality of thinlayers.

A pixel definition layer PXL and the organic light emitting diode OLEDare disposed on the third insulating layer 30. The organic lightemitting diode OLED includes an anode AE, a first common layer CL1, anorganic light emitting layer EML, a second common layer CL2, and acathode CE, which are sequentially stacked one on another. The anode AEis connected to the output electrode DE through a third contact hole CH3formed through the third insulating layer 30. Positions of the anode AEand the cathode CE may be changed with respect to each other, accordingto the light emission direction of the organic light emitting diodeOLED, and positions of the first and second common layers CL1 and CL2may be changed with respect to each other.

The anode AE is disposed on the second insulating layer 30. The pixeldefinition layer PXL is provided with an opening OP formed to expose aportion of the anode AE. The area in which the anode AE is disposed isdefined as a light emitting area LA. The first common layer CL1 isdisposed on the anode AE. The common layer CL1 is disposed not only inthe light emitting area LA, but also in the non-light emitting area NLAadjacent to the light emitting area LA. The first common layer CL1includes a hole injection layer. The first common layer CL1 may furtherinclude a hole transport layer.

The organic light emitting layer EML is disposed on the first commonlayer CL1. The organic light emitting layer EML is disposed only in anarea corresponding to the opening OP. The second common layer CL2 isdisposed on the light emitting layer EML. The second common layer CL2includes an electron injection layer. The second common layer CL2 mayfurther include an electron transport layer. The cathode CE is disposedon the second common layer CL2. The cathode CE is disposed not only inthe light emitting area LA, but also in the non-light emitting area NLA.

A sealing layer ECL is disposed on the cathode CE. The sealing layer ECLis overlapped with the light emitting area LA and the non-light emittingarea NLA. The sealing layer ECL includes an organic layer and/or aninorganic layer. According to another embodiment, a fourth insulatinglayer (not shown) may be further disposed between the cathode CE and thesealing layer ECL to provide a planarized surface. In addition, thesealing layer ECL may be replaced with a sealing substrate.

Although not shown in figures, the switching thin film transistor TR-Smay have the same structure as that of the driving thin film transistorTR-D. In addition, two electrodes of the capacitor Cap may be disposedon the first, second, and third insulating layers 10, 20, and 30.

The elastic modulus of the display panel DP is determined depending onthe elastic modulus of each of the base substrate SUB, the firstinsulating layer 10, the second insulating layer 20, the thirdinsulating layer 30, and the sealing layer ECL. The elastic modulus ofthe display panel DP, which is calculated on the basis of the elasticmodulus of each of the base substrate SUB, the first insulating layer10, the second insulating layer 20, the third insulating layer 30, andthe sealing layer ECL, is in a range from about 1 GPa to about 10 GPa.According to some embodiments, the elastic modulus of the display panelDP may be in a range from about 4 GPa to about 6.5 GPa.

The elastic modulus of the adhesive member AM is determined according toits composition and/or composition ratio. For example, the elasticmodulus of the pressure sensitive adhesive sheet is changed depending onthe composition ratio of the polymer, the cross-linking agent, and theresin. The elastic modulus of the adhesive member AM is in a range fromabout 0.01 MPa to about 1 MPa.

The elastic modulus of the adhesive member AM may be set to be in theabove-mentioned range at a temperature from about −45° C. to about 90°C., by adjusting the composition ratio of the polymer, the cross-linkingagent, and the resin.

The elastic modulus of the outer member OSM may set based on the layerstructure and the material of the outer member OSM. In other words, thetouch screen, the optical member, the window member, and the protectivemember may have different elastic modulus. In the present exemplaryembodiment, the elastic modulus of the outer member OSM may be in arange from about 1 GPa to about 10 GPa, regardless of what type of outermember is included. For example, the elastic modulus of the outer memberOSM may be in a range from about 2 GPa to about 7 GPa.

According to the present exemplary embodiment, the elastic modulus ofthe adhesive member AM may be in a range from about 1/1000000 to about1/1000, with respect to the elastic modulus of the display panel DPand/or the outer member OSM. Particularly, the elastic modulus of theadhesive member AM may be in a range from about 1/600000 to about1/4000, with respect to the elastic modulus of the display panel DP. Inaddition, the elastic modulus of the adhesive member AM may be in arange from about 1/700000 to about 1/2000 with respect to the elasticmodulus of the outer member OSM.

FIGS. 5A and 5B are cross-sectional view showing neutral planesoccurring in flexible display devices, when the flexible display devicesare bent. FIG. 6 is a graph showing strain applied to the flexibledisplay devices shown in FIGS. 5A and 5B. Hereinafter, a relationbetween a ratio of the elastic modulus of the adhesive member AM to theelastic modulus of the display panel DP and the outer member OSM, and astrain of the display device will be described with reference to FIGS.5A and 5B and 6.

FIGS. 5A and 5B show the cross-sectional views corresponding to the lineI-I′ shown in FIG. 1, of a comparative display device and an exemplarydisplay device. In addition, FIGS. 5A and 5B show the display devicesbent such that different portions of the non-display surface NDS becomecloser to each other. FIGS. 5A and 5B show the bending axis PA and areference line RA extending from the bending axis PA and vertical to thedisplay surface DS. The bending direction of the display device shouldnot be limited thereto or thereby, and thus the display device may bebent such that different portions of the non-display surface NDS becomeadjacent to each other.

An adhesive member AM-S of the comparative display device shown in FIG.5A has an elastic modulus exceeding about 1/1000 of the elastic modulusof each of the display panel DP-S and the outer member OSM-S. Thecomparative display device includes the adhesive member AM-S having theelastic modulus of about 1/100 of the elastic modulus of each of thedisplay panel DP-S and the outer member OSM-S.

The adhesive member AM of the exemplary display device shown in FIG. 5Bhas the elastic modulus smaller than about 1/1000 of the elastic modulusof each of the display panel DP and the outer member OSM. The exemplarydisplay device includes the adhesive member AM having the elasticmodulus of about 1/10000 of the elastic modulus of each of the displaypanel DP and the outer member OSM. The display panel DP has the elasticmodulus of about 6 GPa, the outer member OSM has the elastic modulus ofabout 5 GPa, and the adhesive member AM has the elastic modulus of about0.5 MPa.

When the comparative display device is bent, one neutral plane NP1occurs. On the neutral plane NP1, a compressive force occurring in thedisplay device is equal to a tensile stress occurring in the displaydevice. Since the elastic modulus of the adhesive member AM-S isrelatively greater than that of the display panel DP-S and the outermember OSM-S, the display device is bent as a one-piece member.

The comparative display device has a predetermined curvature ratio Rbwhen being bent. When the exemplary display device has a predeterminedthickness Tt, the exemplary display device has the strain (S)represented by the following Equation. The thickness Tt of the exemplarydisplay device is equal to a sum of thicknesses T1, T2, and T3 of thedisplay panel DP-S, the outer member OSM-S, and the adhesive memberAM-S.

$\begin{matrix}{S = {\frac{{\pi \left( {{Rb} + {T{t/2}}} \right)} - {\pi Rb}}{\pi Rb} - \frac{Tt}{2Rb}}} & {Equation}\end{matrix}$

When the exemplary display device is bent, neutral planes NP10 and NP20are formed. Different neutral planes NP10 and NP20 occur in the displaypanel DP and the outer member OSM. This is because the display panel DPand the outer member OSM are partially separated from each other by thestress applied to the adhesive member AM, when the exemplary displaydevice is bent. Although not shown in figures, a neutral plane may occurin the adhesive member AM.

The display panel DP and the outer member OSM have independent strainsapplied thereto. The display panel DP has a strain corresponding to thethickness T10 thereof, and the outer member OSM has a straincorresponding to the thickness T20 thereof. The display panel DP and theouter member OSM each have a small amount of strain in consideration ofthe thickness Tt of the display device.

In the present exemplary embodiment, the thickness T10 of the displaypanel DP is in a range from about 30 micrometers to about 40micrometers, the thickness T20 of the outer member OSM is in a rangefrom about 40 micrometers to about 120 micrometers, and the thicknessT30 of the adhesive member AM is in a range from about 20 micrometers toabout 100 micrometers. The thickness T20 of the outer member OSM variesdepending on its type.

FIG. 6 shows a first graph GR1 representing the strain of thecomparative display device shown in FIG. 5A and second graphs GR2-1 andGR2-2 representing the strain of the exemplary display device shown inFIG. 5B. The first graph GR1 and the second graphs GR2-1 and GR2-2represent the strain with respect to the reference lines RA.

According to the first graph GR1, the outer member OSM-S of thecomparative display device has a relatively large strain, according tothe tensile force, and the display panel DP-S has the relatively largestrain, according to the compressive force. According to the secondgraphs GR2-1 and GR2-2, the strain of the exemplary display device,according to the tensile force and the compressive force, are smallerthan those of the comparative display device. As represented by pointsA1, A2, A3, and A4 of the first graph GR1, and points A10, A20, A30, andA40 of the second graphs GR2-1 and GR2-2, the strain occurring in theexemplary display device is smaller than that of the comparative displaydevice, at corresponding points.

Although the exemplary display device is bent, the strain applied to thedisplay panel DP is relatively small, and thus, internal components,e.g., the driving thin film transistor TR-D and/or the organic lightemitting diode OLED of the display panel DP are not damaged. Inaddition, the display panel DP and the outer member OSM are notphysically separated from each other.

According to another exemplary embodiment, when the display devices arebent in an opposite direction, the first graph GR1 and the second graphsGR2-1 and GR2-2 are left and right reversed with respect to thereference line RA.

FIG. 7 is a cross-sectional view showing a flexible display deviceaccording to an exemplary embodiment of the present disclosure. In FIG.7, the same reference numerals denote the same elements in FIGS. 1 to 6,and thus, detailed descriptions of the same elements will be omitted.

Referring to FIG. 7, the display device according to the presentexemplary embodiment includes a flexible display panel DP (hereinafter,referred to as a display panel), a first outer member OSM1 disposed on adisplay surface DS of the display panel DP, and a second outer memberOSM2 disposed on a non-display surface NDS of the display panel DP. Thedisplay panel DP and the first outer member OSM1 are coupled to eachother by a first adhesive member AM1. The display panel DP and thesecond outer member OSM2 are coupled to each other by a second adhesivemember AM2.

The first outer member OSM1 may include at least one of a touch screenpanel, an optical member, and a window member. The second outer memberOSM2 may include a protective member.

The touch screen panel senses an external input in various ways, such asan electrostatic capacitive mode, a resistive mode, an electromagneticinduction mode, etc. The optical member includes a polarization memberand a phase difference compensation member. The touch screen panel andthe optical member are integrally formed as a single unit. Thepolarization member and the phase difference compensation member form abase substrate of the touch screen panel.

In the present exemplary embodiment, the touch screen panel has athickness of about 40 micrometers to about 60 micrometers, and theoptical member has a thickness of about 70 micrometers to about 120micrometers. The touch screen panel has an elastic modulus of about 2GPa to about 3 GPa and the optical member has an elastic modulus ofabout 4 GPa to about 5 GPa.

The window member may be a flexible plastic film or a thin glasssubstrate. The window member may have a multi-layer structure. Inaddition, a functional layer is coated on an outer surface of the windowmember. The functional layer includes at least one of ananti-fingerprint coating, an anti-reflection coating, an anti-glarecoating, and a hard coating. The window member has a thickness of about50 micrometers to about 100 micrometers and an elastic modulus of about3 GPa to about 6 GPa.

The protective member may be, for example, a flexible plastic film. Theprotective member may have a multi-layer structure. The protectivemember may have a thickness of about 25 micrometers to about 100micrometers and an elastic modulus of about 6 GPa to about 7 GPa.

When the display device is bent, neutral planes NP10, NP20, and NP30 areformed. The neutral planes NP10, NP20, and NP30 are respectively definedin the display panel DP, the first outer member OSM1, and the secondouter member OSM2. When the display panel is bent, the display panel DPand the first outer member OSM1 are partially decoupled from each otherby the stress applied to the first adhesive member AM1, and the displaypanel DP and the second outer member OSM2 are partially decoupled fromeach other by the stress applied to the second adhesive member AM1.

FIGS. 8A to 8F are cross-sectional views showing flexible displaydevices according to exemplary embodiments of the present disclosure.The display devices shown in FIGS. 8A to 8F have different layerstructures from each other. In FIGS. 8A to 8F, the same referencenumerals denote the same elements in FIGS. 1 to 7, and thus, detaileddescriptions of the same elements will be omitted.

Referring to FIG. 8A, the display device includes a display panel DP, aprotective PF disposed on a non-display surface NDS of the display panelDP, and a touch screen panel TSP, an optical member LF, and a windowmember WM, which are sequentially stacked on the display surface DS. Afunctional layer FC is disposed on an upper surface of the window memberWM.

Among the protective member PF, the display panel DP, the touch screenpanel TSP, the optical member LF, and the window member WM (membershereinafter), adhesive members AM are disposed. The adhesive members AMcouple adjacent members to each other.

The adhesive members AM have an elastic modulus of about 1/1000000 toabout 1/1000 of the elastic modulus of the members connected thereby.When the display device is bent, a neutral plane occurs in each of themembers. Each of the members has the strain corresponding to itsthickness. Accordingly, although the thickness of the display deviceincreases, the strain of each of the protective member PF, the displaypanel DP, the touch screen panel TSP, the optical member LF, and thewindow member WM is not varied substantially.

FIG. 8B shows the display device shown in FIG. 8A, from which theoptical member LF is removed, FIG. 8C shows the display device shown inFIG. 8A, from which the touch screen panel TSP is removed, and FIG. 8Dshows the display device shown in FIG. 8, from which the protectivemember PF is removed. FIG. 8E show the display device shown in FIG. 8A,in which the optical member LF is integrated in the touch screen panelTSP. FIG. 8F shows the display device shown in FIG. 8A, in which aposition of the touch screen panel TSP is changed.

Although the exemplary embodiments of the present invention have beendescribed, it is understood that the present invention should not belimited to these exemplary embodiments but various changes andmodifications can be made by one ordinary skilled in the art within thespirit and scope of the present invention as hereinafter claimed.

What is claimed is:
 1. A flexible display device comprising: a flexibledisplay panel; a flexible outer member disposed on the flexible displaypanel; and an adhesive member disposed between the flexible displaypanel and the flexible outer member, wherein, when the flexible displaydevice is bent, stress is applied to the adhesive member so as to atleast partially decouple a first neutral plane formed in the flexibledisplay panel and a second neutral plane separate from the first neutralplane formed in the flexible outer member.
 2. The flexible displaydevice of claim 1, wherein the elastic modulus of the adhesive member isfrom 1/1000000 to 1/1000 of an elastic modulus of each of the flexibledisplay panel and the flexible outer member.
 3. The flexible displaydevice of claim 2, wherein: a compressive stress applied to the firstneutral plane is substantially equal to a tensile stress applied to thefirst neutral plane; and a compressive stress applied to the secondneutral plane is substantially equal to a tensile stress applied to thesecond neutral plane.
 4. The flexible display device of claim 3, whereinthe flexible outer member comprises a protective member disposed on anon-display surface of the display panel, the non-display surfaceopposing the display surface.
 5. The flexible display device of claim 3,wherein the elastic modulus of the adhesive member is in a range of 0.01MPa to 1 MPa.
 6. The flexible display device of claim 3, wherein theelastic modulus the adhesive member is in a range of 0.01 MPa to 1 MPa,at a temperature of in a range of −45° C. to 90° C.
 7. The flexibledisplay device of claim 6, wherein: the adhesive member comprises apressure sensitive adhesive sheet that comprises a polymer, across-linking agent, and a resin; and the polymer comprises anacryl-based polymer, a silicon-based polymer, a urethane-based polymer,or any combination thereof.
 8. The flexible display device of claim 5,wherein an elastic modulus of the flexible display panel is in a rangeof 1 GPa to 10 GPa.
 9. The flexible display device of claim 5, whereinthe elastic modulus of the flexible outer member is in a range of 2 GPato 7 GPa.
 10. The flexible display device of claim 1, wherein theflexible display device is configured to bend.